The value of using heterogeneous detector groups for the development of time-of-flight (TOF) positron emission tomography (PET) systems

Objective. Much recent attention on positron emission tomography (PET) is the development of time-of-flight (TOF) systems with ever-improving coincidence time resolution (CTR). This is because, when all other factors remain the same, a better CTR leads to images of better statistics and effectively increases the sensitivity of the system. However, detector designs that aggressively improve the CTR often compromise the detection efficiency (DE) and offset the benefit gained. Under this circumstance, in developing a TOF PET system it may be beneficial to employ heterogeneous detector groups to balance the overall CTR and DE of the system. In this study, we examine the potential value of this system design strategy by considering two-dimensional systems that assume several representative ways of mixing two detector groups. Approach. The study is based on computer simulation and specifically considers medium time-resolution (MTR) detectors that have a 528 ps CTR and high time-resolution (HTR) detectors that have a 100 ps CTR and a DE that is 0.7 times that of the MTR detector. We examine contrast recovery, noise, and subjective quality of the resulting images under various ways of mixing the MTR and HTR detectors. Main results. With respect to the traditional configuration that adopts only the HTR detectors, symmetric heterogeneous configurations may offer comparable or better images while using considerably fewer HTRs. On the other hand, asymmetric heterogeneous configurations may allow the use of only a few HTRs for improving image quality locally. Significance. This study demonstrates the value of the proposed system-level design strategy of using heterogeneous detector groups for achieving high effective system sensitivity by factoring into the tradeoff between the CTR and DE of the detector.